Maxima Function
assoc (key, list, default)
assoc(key,list)
This function searches for the key in the left hand side of the input list
of the form [x,y,z,...] where each of the list elements is an expression of
a binary operand and 2 elements. For example x=1, 2^3, [a,b] etc.
The key is checked againts the first operand. assoc returns the second
operand if the key is found. If the key is not found it
either returns the default value. default is optional
and defaults to false.